Mass-loss from massive globular clusters in tidal fields

Abstract

ABSTRACT Massive globular clusters lose stars via internal and external processes. Internal processes include mainly two-body relaxation, while external processes include interactions with the Galactic tidal field. We perform a suite of N-body simulations of such massive clusters using three different direct-summation N-body codes, exploring different Galactic orbits and particle numbers. By inspecting the rate at which a star’s energy changes as it becomes energetically unbound from the cluster, we can neatly identify two populations we call kicks and sweeps that escape through two-body encounters internal to the cluster and the external tidal field, respectively. We find that for a typical halo globular cluster on a moderately eccentric orbit, sweeps are far more common than kicks but the total mass-loss rate is so low that these clusters can survive for tens of Hubble times. The different N-body codes give largely consistent results, but we find that numerical artefacts may arise in relation to the time-step parameter of the Hermite integration scheme, namely that the value required for convergent results is sensitive to the number of particles.